The present invention relates to a method for determining measuring positions and to a method for planning measuring tracks as well as to a method for measuring an object or a part thereof, and to a device for measuring an object or a part thereof. A method of that kind for determining measuring positions is already known from Thorsten Glaschke, “Schnelle 3D-Digitalisierung” Fast 3D Digitization], Spektrum No. 74, p. 10, 1999, (the “Glaschke article”). A method of that kind and a device of that kind for measuring an object or a part thereof are already known from the Glaschke article as well.
Surface measurement via optical measuring systems, in particular using active vision systems, is gaining more and more importance in industry. For quality assurance and in reverse engineering, tactile 3D coordinate measuring machines have already been used for a long time. Tactile measuring systems offer active measurement strategies for standard measuring tasks (for example, the measurement of bore holes).
Active measurement provides for automatic, fast and collision-free measuring. Moreover, by taking into account the technical boundary conditions of a sensor during active measurement (for example, measuring volume, measuring angle), the quality of a measurement is ensured even if a semi-skilled worker and not an experienced measuring engineer carries out the measurement.
Optical sensors can perform measurements much faster and be used closer to the manufacture than tactile measuring techniques which is why they are becoming more and more widespread. For reverse engineering in vehicle design, optical sensors have frequently already replaced the tactile measuring technology. There, physical 1:5 or 1:1 models of vehicle bodies are digitized to make available the data required for the design in CAD systems, for virtual reality applications or for rapid prototyping. However, active measurement using optical sensors is not yet in use.
An essential requirement for active measurement is the automatic determination of optical measuring positions.
An active measuring system based on a laser triangulation sensor which is positioned via a coordinate measuring machine has already been proposed in the Glaschke article. In this connection, first of all, the total measuring volume of the object to be measured must be entered by the operator; then, the measuring system carries out a rough measurement which is used for determining suitable measuring positions and for planning the measuring tracks for the actual measurement. No details are given on the implementation of this planning. Subsequently, the laser triangulation sensor is positioned via the coordinate measuring machine and the measurement of the object to be measured is carried out. This measuring system needs a high-precision and expensive positioning unit and is therefore only used in air-conditioned measuring rooms.
As a general principle, the determination of measuring positions and the planning of measuring tracks for active object measurement requires a priori knowledge. A suitable set of suitable sensor positions is to be determined from a set of known reference points on the surface of the object to be measured. In the object measuring technique set forth in the Glaschke article, the reference points are determined via the rough measurement preceding the actual measurement. No information can be gathered from the Glaschke article on how to determine suitable sensor positions (measuring positions) and on how to plan a suitable sequence of approaching these sensor positions based on the knowledge of the reference points.